A block copolymer comprising a conjugated diene and a vinyl aromatic hydrocarbon is different from natural rubbers and conventional synthetic rubbers. The block copolymer has strength and elastic characteristics which is equal to vulcanized elastomers at room temperature, without having been vulcanized by the use of a vulcanization agent, an accelerator and a filler such as carbon black, etc. The block copolymer also exhibits good processability which is similar to that of thermoplastics at high temperatures, and therefore it is now utilized in very wide scope of fields by the utilization of these characteristics. Examples of the applications of the block copolymer may include- an injection molded products such as hoses, footwares, window frames, vessels, toys, domestic articles, etc., as well as extrusion molded products, blow molded products, cohesives, adhesives, modified asphalts, modified thermoplastic resins, thermosetting resins, vulcanized rubbers, etc.
In the various uses described above, the adhesives has been used in various products, such as an adhesive tape, a label, etc. For the application of an adhesive onto tapes, there has generally been a method employed in which an adhesive solution containing an adhesive dissolved in a solvent is coated onto a substrate by means of rollers coating, spray, etc. However, the use of such solvents involve many problems with respect to pollution of the atmosphere, fire, work environment, hygiene, etc., and it is recently regarded as being a serious social problem. Accordingly, as the means for solving such inconvenience, a hot melt adhesive of the non-solvent type has recently attracted attention.
As the base polymer for a hot melt adhesives, there have been employed various polymers such as ethylene-vinyl acetate copolymer, a block copolymer comprising a conjugated diene and a vinyl aromatic hydrocarbon, ethylene-.alpha.-olefin copolymer, polyester resin, etc., but among the above, the block copolymer is preferably used because of having a relatively good balance between tackiness and creep resistance. For example, Canadian Patent No. 742758 and U.S. Pat. No. 3427269 disclose adhesive compositions containing a linear-chain block copolymer such as polystyrene-polybutadiene-polystyrene or polystyrenepolyisoprene-polystyrene, etc. Also, Japanese Patent Publication Examined No. 49958/1981 discloses a hot melt adhesive composition comprising a branched-chain block copolymer of (polystyrene-polybutadiene).sub.n X.
On the other hand, a primary use of the block copolymer is to use it in combination with inorganic fillers or organic fillers, thermoplastic resins, etc. For example, U.K. Patent No. 1092563, U.S. Pat. Nos. 3459830 and 4107124 describe the use of compositions comprising a thermoplastic resin such as polystyrene, polyethylene, etc., a softener such as a naphthenic oil, etc., an inorganic filler such as clay, calcium carbonate, etc., formulated in footwares. Also, U.K. Patent No. 1105585, U.S. Pat. No. 3637554 and U.K. Patent No. 1077769 describe methods for improving impact resistance by formulating the above-described block copolymer in polystyrene or a rubber-modified polystyrene. Similarly, U.S. Pat. Nos. 3294868 and 3459831, Japanese Patent Publications Examined Nos. 5067/1971 and 1867/1971, and West Germany Patent Publication No. 2255930 describe attempts to improve the characteristics by formulating the above-described block copolymer in polypropyrene, polyethylene, an acrylic resin, a vinyl chloride resin, and a polyphenylene ether resin, respectively.
It has been known that the properties of a bituminous material which is brittle and susceptible to impact destruction at low temperature or susceptible to plastic deformation at high temperature can be improved to increase its durability by mixing therewith a natural rubber or a synthetic rubber such as styrene-butadiene rubber, a nitrile rubber, etc., and such compositions have been already utilized for civil engineering, construction, industry, typically uses for roads in Japan or in various foreign countries.
For preparing a rubber-mixed bituminous composition, there is a method in which a rubber is mixed with a bituminous material on open rollers to prepare a masterbatch having a high rubber content and the masterbatch is mixed with a bituminous material, heated and melted to be dissolved therein. In another method, a rubber in a form of powder or latex is mixed with a bituminous material heated and melted to be dissolved therein. Recently in particular, a bituminous composition mixed with a block copolymer having an excellent solubility characteristic in the composition during mixing and being relatively lower in viscosity at high temperature, is preferably used rather than a bituminous composition mixed with a natural rubber or a synthetic rubber which has been previously conventionally used. For example, U.K. Patent No. 1177725 discloses a bituminous composition which contains a block copolymer of a vinyl aromatic compound and a conjugated diene compound dissolved therein.
However, in the use of adhesives, since the block copolymer comprising styrene and butadiene is inferior in initial tackiness the use of a block copolymer comprising styrene and isoprene having excellent characteristics for an adhesive tape and an adhesive label for which initial tackiness is particularly demanded, has recently been increased. However, a block copolymer comprising styrene and isoprene will be changed in viscosity and physical properties by cleavage of molecular chains caused by heat degradation, when the adhesive composition is left to stand at high temperature for a long period of time. Accordingly, an improvement is still desired.
On the other hand, a block copolymer comprising styrene and butadiene, though free from cleavage of molecular chains, has the problem in that it is inferior in initial tackiness. Various investigations have been conducted in the prior art concerning improving the initial tackiness of a block copolymer comprising styrene and butadiene. For example, U.K. Patent No. 1447419 discloses a method in which a hydrogenated resin of an aromatic petroleum resin prepared by hydrogenating a petroleum resin obtained by polymerization of petroleum distillates containing a polymerizable aromatic hydrocarbon as a main component at a ratio of 40 to 80% of hydrogenation in the nucleus of aromatic components, is used as the tackifier resin. On the other hand, in Japanese Patent Publication Unexamined No. 2375/1982, there is disclosed a method in which a hydrogenated resin having a softening point of 50 to 160 .degree. C. is used. The resin is prepared by heating a distillate at 220 .degree. C. to 320 .degree. C. and copolymerizing it, and further subjected to hydrogenation. The distillate has a concentration of dicyclopentadiene concentration of 10 to 70% and a concentration of tetrahydroindene and/or vinylcyclohexene of 30 to 80%. The distillate is obtained by distilling off most of the vinyl norbornene which is the main product contained in the reaction mixture resulting from the Diels-Alder reaction of 1,3-butadiene and cyclopentadiene. However, even according to such a method, an improvement of initial tackiness of the resin formed is still unsatisfactory and an improvement is still desired.
Also, U.K. Patent No. 1405786 describes a method in which polystyrene-hydrogenated polybutadiene-polystyrene or polystyrene-hydrogenated polyisoprene-polystyrene is used for improving the adhesive properties of the composition at relatively high temperature conditions. Among them are adhesive compositions which are a block copolymer comprising a vinyl aromatic compound and a conjugated diene compound. However, the compositions described in the patent have the problem of being inferior in initial tackiness.
A composition comprising a block copolymer of a vinyl aromatic hydrocarbon and a conjugated diene formulated in a thermoplastic resin is generally inferior in high temperature moldability, and when molding is performed at a relatively high temperature for the purpose of improving productivity during the molding of said composition, which results in the ensuing problems such as the impact resistance being abruptly lowered or that the desired performance cannot be obtained even when molding is being conducted by formulating a block copolymer in an engineering plastic, etc., for which molding at high temperature is required.
Accordingly, for the purpose of improving high temperature moldability, it has been attempted to formulate in a thermoplastic resin, a block copolymer obtained by hydrogenating a block copolymer of a vinyl aromatic hydrocarbon and a conjugated diene to convert a conjugated diene polymer block to a saturated olefin polymer block. For example, U.K. Pat. Nos. 1581167 and 1559052 describe a composition, in which a block copolymer having 80% or more, more preferably 99% or more of its aliphatic double bond portions which originated from a hydrogenated conjugated diene, is formulated in an engineering plastic. However, in such a composition, the compatibility of the hydrogenated block copolymer with the thermoplastic resin is inferior, which results in such problems as the possible occurrence of a layer peel-off phenomenon of the molded product of the composition, depending upon the formulated amount. Also, due to having an inferior lower temperature characteristic, no desired performance can be exhibited at lower temperatures.
Further, in a composition comprising a bituminous material mixed with a block copolymer, when dissolving is conducted at a temperature which is higher than a conventional dissolving temperature in order to improve the productivity during processing by further shortening the dissolving time, or when the dissolving time is shortened during the mixing of a block copolymer having a relatively higher molecular weight which can be dissolved only with difficulty, or when processing and working are practiced at higher temperatures in order to improve the workability by lowering the viscosity after mixing, the problem involved is that the block copolymer suffers from heat degradation to provide a bituminous composition having none of the desired physical properties. In order to improve the heat aging properties of the block copolymer, it has also been attempted to use a completely hydrogenated block copolymer in which its aliphatic double bond portions which originated from the butadiene compound in the block copolymer is hydrogenated to 90% or more, generally to substantially 100%. However, a composition which comprises such a completely hydrogenated block copolymer is inferior in low temperature properties, and would thus have the problem of the flexibility thereof being worsened at cold temperatures.
In view of the state of the art described above, the present inventors have studied intensively to improve initial tackiness and heat treatment performance at high temperature of an adhesive composition by the use of a block copolymer comprising an aromatic compound and a conjugated diene compound, and to obtain a composition having excellent heat aging resistance, moldability at high temperature, compatibility, impact resistance and low temperature properties by the use of a thermoplastic resin, inorganic or organic filler, etc., in combination with the block copolymer, and further to obtain a bituminous composition having excellent low temperature properties and heat aging resistance and also having a good softening point, penetration and strength. The present inventors consequently have found that these purposes can be accomplished by using a block copolymer which is specifically hydrogenated at its aliphatic double bond portions which originated from the conjugated diene compound. And accordingly, the present invention has been completed.